Plastic industry has brought convenience to human life, while it has also caused severe environmental problems. Currently, the total annual plastic production is about 140 million tons, with 50% to 60% of which is abandoned. The most severe environmental pollution in China is concentrated on the usage of disposable products, such as tableware, plastic packaging boxes, bags, films and medical plastic products.
Nowadays disposable products sold in market are mainly made of foaming materials such as polyethylene-starch blend and polyphenylene, polypropylene-starch blend and polyphenylene, polypropylene/starch blend and polyphenylene, none of these foam disposable products however will completely degrade into CO2 and H2O in biodegradation processes. For example, in polyethylene-starch foam, since starch is physically mixed in polyethylene rather than attached to the large molecular chain of polyethylene, degradation of the starch will not cause the polyethylene to degrade, therefore, though from appearance the foam product is mashed after degradation processes, the large molecular polyethylene is still there and only in smaller geometry size, which would in fact accelerate its influence on soil and cause environmental pollution.
Polyhydroxyalkanoates, for example poly(3-hydroxylbutyrate-co-4-hydroxylbutyrate) P(3HB-co-4HB), poly(3-hydroxylbutyrate-co-3-hydroxyvalerate) P (3HB-co-3HV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) P(3HB-co-3HHx) and poly(3-hydroxybutyrate-co-3-hydroxydecanoate) P(3HB-co-3HD) are all possess good flexibility and will completely degrade into CO2 and water after 3˜6 months under nature environments such as sea water, sewage or soil with high bacteria density. Additionally, these polymers are manufactured in fermentation processes which are clean and environmental friendly.
However, since the above-mentioned polyhydroxyalkanoates are normally semi-crystalline thermoplastic polyester compound which have low crystallinities and low melting points, the crystallization rate is low and adhesion may occur during cooling, which make it difficult to collect the finished article and the yield is very low. In the meantime, cost for producing these bio-polyesters is relatively high at present.
Therefore, there is a need to use the bio-degradable characteristics and overcome the defects such as low crystallinities and melting points associated with the above-mentioned polyhydroxyalkanoates to find a cost effective bio-degradable foam which is suitable for batch production by available foam plastic plants on market, and therefore can be widely used in the packaging industry.